The present invention relates to a technique which can be applied mainly to a self-luminescent gas discharge display panel comprising a glass substrate bearing a conductive layer and an insulating layer and, further, to a thermal head comprising glass having a conductive layer and a heater used in a rear window of automobiles. More particularly, the present invention relates to a method for forming a conductive or insulating layer in a pattern form on a glass substrate by photolithography.
The present invention will now be described by taking a DC-type gas discharge display panel as an example.
FIG. 1 is an embodiment of the construction of a DC-type plasma display panel (hereinafter referred to as "PDP"). In the DC-type PDP, a flat front plate (not shown) and a back plate (not shown) each formed of an insulating material, such as glass, are provided parallel to and so as to face each other. A barrier 1 is fixed on the inner side of the back plate in a direction orthogonal to the back plate. This barrier 1 serves to provide a certain gap between the front plate and the back plate. A cathode 2 is formed on the inner side of the front plate. On the other hand, an anode bus 3 and a resistor 4 are provided on the inner side of the back plate in a direction orthogonal to the cathode 2. Further, a pad 5 is provided on the resistor 4, and a fluorescent screen 6 is provided adjacent to the side face of the pad 5. The anode bus 3 is generally formed of gold or silver, the resistor 4 is generally formed of ruthenium, and the cathode 2 is generally formed of nickel or the like.
In the DC-type PDP having the above construction, the application of a predetermined voltage from a direct current power supply across the pad 5 and the cathode 2 creates an electric field, causing discharge within each discharge cell 7 defined by the front plate, the back plate, and the barrier 1. The discharge produces ultraviolet light which renders the fluorescent screen 6 luminous, and a viewer perceives the light passing through the front plate.
Screen printing is known as a method for forming an anode bus 3 and a barrier 1 on a back plate of PDP having a structure shown in FIG. 1. Another method known in the art is photolithography wherein a low-melting glass powder and a conductive or insulating powder are added to a photosensitive solution using an organic solvent as a solvent system to prepare a photosensitive slurry which is then coated on a glass substrate, dried, exposed, and developed with an aqueous alkaline solution to form a desired pattern. Further, as a method for forming the anode bus 3, a technique is known wherein a conductive paste is screen-printed to provide a solid print which is fired and then etched.
In an attempt to increase the size and fineness in PDP, the possible finest anode bus and barrier attained by the conventional screen printing are about 100 .mu.m in width. Further, the conventional method has a problem that elongation and strain in a screen plate render the pattern inaccurate. This problem brings about a local difference in resistance between the anode bus and the pad, resulting in uneven discharge characteristics. On the other hand, the technique where an anode bus is formed by etching suffers from a complicated production process and, in addition, poses a problem of wastewater treatment involved in the etching.
In view of the above problems, photolithography is considered suitable for the formation of a conductive or insulating layer. The above conventional photolithography involves an environmental problem, which unavoidably occurs in handling a solvent, and a problem of wastewater treatment associated with the development with an aqueous alkaline solution.